Typically the treated water from a septic system, e.g., an aerobic wastewater treatment system (AWTS) is pumped from a holding vessel, e.g., a pump tank, to a drip or spray irrigation field. In a drip field, there is an array of lines, generally buried, each of which has a plurality of drip emitters which have small orifices which discharge small amounts of water from the lines into the drip field when the pump is in operation. A typical layout of a drip irrigation system connected to an AWTS is shown and described in U.S. Pat. No. 8,715,492, incorporated herein by reference for all purposes.
The drip emitters used in typical drip irrigation systems generally fall into two classes: pressure compensating (PC) emitters and non-pressure compensating (NPC) emitters. This designation of emitters is somewhat misleading since all emitters are pressure compensating to some degree. However, for purposes of defining the differences, PC emitters are those that are designed to discharge water at a uniform rate over a wide range of water pressures. By example, PC emitters give essentially the same flow at 3.0 bar (45 psi) as they do at 1.0 bar (15 psi). NPC emitters are dependent to a certain extent upon line pressure. However, provided line pressure is adequate, generally speaking, NPC emitters and PC emitters both operate satisfactorily to deliver substantially constant flow.
Regardless of the types of drip emitters used in a typical drip irrigation system, as noted above, they all have small orifices which can become plugged. It will be recognized that when the pump is operating to force water through the drip emitters, the flow rate through the lines or conduits is relatively low because of flow through the emitters, back pressure regulators, etc.
This low flow rate through the lines can lead to the accumulation of wastewater sludge, dirt, debris, and the like in the lines which can in certain instances plug the emitters and interferes with the operation of the irrigation system. Accordingly, many jurisdictions require that the lines in the drip field be periodically flushed at a high flow rate relative to the normal flow rate used when in the irrigation mode.